Stenosis, for example, of the aortic valve leads to an abnormal turbulence during ejection of blood through it from the left ventricle, so it is a systolic murmur because it occurs during the phase of contraction (systole), preceding the second heart sound at the closure of the valve. Valves may become leaky, allowing backflow (incompetence), or they may become stiff and narrow (stenosis). They are most often caused by any departure from the crisp sounds described here which reflect equally crisp function of the valves. Heart murmurs are soft sounds, like those made during a forcible expiration with the mouth open. With experience, the two sounds can be distinguished by pitch and intensity also at a resting heart rate there is a longer interval between beats than between the two sounds. The second heart sound is produced by closure of the aortic and pulmonary valves (between the ventricles and their respective arteries), and is often described as ‘dup’ the ‘d’ reflecting the louder aortic valve closure preceding the quieter tricuspid valve closure ‘p’. Deep inspiration widens the split between mitral and tricuspid closure: ‘lu-ub’. It is often described as ‘lub’ the ‘l’ reflecting the louder mitral valve closure preceding the quieter tricuspid valve closure ‘b’. The first heart sound is produced by closure of the two atrio–ventricular valves, when the ventricles start to contract. The left side of the heart develops a higher pressure than the right side, which means that the sounds produced there, by the mitral (bicuspid) valve between atrium and ventricle, and the aortic valve at the exit from the ventricle, are generally louder and precede the sounds produced from the equivalent valves on the right side (tricuspid and pulmonary valves). The sounds arise from the brief turbulence of blood flow occurring just as a valve closes. Heart sounds With an ear applied to the chest - or more usually, with a stethoscope - it is normally possible to detect two sounds in every heart beat, which are produced when the valves of the heart close.
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